The ATtiny85 Breakout board is the smallest Arduino Compatible board! It measures less that 1 square inch and has an onboard microUSB port! With 6 I/O pins an onboard voltage regulator and 3 Power Pins, this is a super awesome way to get Arduino based projects into the tiniest of places! Just plug in a microUSB cable to your computer and program using the Arduino software.

6 I/O Pins: 2 pins (P3 & P4) are tied to USB (This means if your program actively communicates over USB they will be in use. If your program does not actively communicate over USB you can use all 6 I/O pins after programming via USB)